The subject matter of the present invention relates generally to rotary casting apparatus for molding hollow articles of synthetic plastic material in a plurality of hollow molds which are each rotated and heated within a fixed oven. In particular, the invention relates to such a rotary casting apparatus having an improved rotation and support means for rotating each of the molds about two perpendicular axes, as well as an improved cooling means for cooling the molds within the oven by injecting cool, moist air into such oven.
While the present rotary casting apparatus can be employed to manufacture other hollow plastic articles, it is especially useful in molding globes for lamp posts and is an improvement on the prior molding apparatus shown in U.S. Pat. No. 3,570,061, granted Mar. 16, 1971, to A. M. Andrews. This prior apparatus was used for molding single articles one at a time in an oven, but it is not suitable for molding a plurality of articles simultaneously because, among other reasons, such oven is rotated to rotate the mold about its second axis. In addition, it has been found that spraying water directly onto the molds by a sprayer nozzle positioned within the oven, as in this prior apparatus, can, under some circumstances, cause bubbles to occur in the molded article apparently due to excess moisture entering the molds. Both of these problems are overcome in the present invention by the improved rotation and support means for the molds which enables the oven to remain stationary and by the improved cooking means which directs moist air into the oven from an external source.
In previous multiple mold rotational casting apparatus employing a stationary oven, the molds are cooled in a separate cooling chamber outside of the oven by spraying water thereon, as shown in U.S. Pat. No. 3,561,060 of Stevens. This results in a much more complicated and expensive apparatus and does not avoid the bubbling problem discussed above. Recently it has been proposed in U.S. Pat. No. 3,574,245 by R. G. Dohm to provide a rotational casting apparatus employing a plurality of molds which are heated and cooled by transmitting heating liquid and cooling liquid to jackets surrounding the molds without using an oven. However, this type of heating and cooling greatly complicates the rotation and support means for the molds because the heating and cooling fluids must pass through rotating shafts forming part of such rotation and support means. The present invention provides an improved multiple mold rotary casting apparatus which is much simpler, more compact and less expensive than these prior apparatus and which produces molded articles of improved quality.